1. Field of the Invention
The invention relates to a machine for producing and/or treating a material web, in particular of paper or board, in which the material web can be guided along a material web guide path by means of at least one material web guide device from a material web production section or material web input section, in order to pass at least one material web treatment device, having an apparatus for forming a transfer strip of the material web and transferring the transfer strip through the machine, it being possible for the material web to be transferred along the material web guide path in that, by means of the apparatus for forming and transferring the transfer strip, a leading transfer strip of the material web is formed and guided through the machine, and the width of the transfer strip is increased to the full material web width (what is known as “tail widening”), and having an apparatus for detecting a break in the material web.
The invention relates further to a method for monitoring the transfer of a material web of paper or board along a material web guide path of a machine for producing and/or treating the material web, the transfer of the material web being carried out in that a leading transfer strip of the material web is guided through the machine and the width of the transfer strip is increased to the full material web width (what is known as “tail widening”).
2. Discussion of Background Information
What is known as web threading in a machine for producing and/or treating a material web, specifically a material web of paper or board, is normally carried out by means of at least one transfer strip, which is divided off from the material web and is then guided through following guide and/or treatment devices. This type of web threading is standard both in papermaking and boardmaking machines having in each case at least one head box, a wet end (in particular wire section and/or press section), and a drying section, possibly one or more processing sections (for example a coating section) and also in paper or board processing machines provided for the off-line treatment of a material web produced in another way, for example what are known as coating machines. In order to form or divide off the transfer strip, diverse devices are known. For example, what are known as strip knock-off devices, water jet cutting devices, laser cutting devices and so on are used. In connection with papermaking machines, use is normally specifically made of what is known as a “couch jet” which, on a wire of the wire section, cuts a strip into the paper web (or board or tissue web), which is then guided through the further sections of the machine, in particular at least one press section and at least one drying section and, if appropriate, at least one treatment section. In the case of transfer devices which are mounted downstream of the drying section, what is known as a tip cutter is used instead of the couch jet. As soon as the transfer strip is running stably through the machine, it is then possible, by using the couch jet on the wire, to move to the “full width”, that is to say approximately from a strip position adjacent to the operator side to the drive side or, vice versa, from a strip position adjacent to the drive side to the operator side, as a result of which the full web width then automatically runs through the machine. In the specialist field, one speaks of what is known as “tail widening” in this connection. This type of web threading or similar type of web threading (for example, the transfer strip could also be formed in a central region of the material web) has also proven worthwhile in relation to all the conventional material web treatment devices, those designed as an online material web treatment device and designed as an off-line material web treatment device, such as press sections, predryer sections, afterdryer sections, coating machines, smoothing units (for example calenders), reelers and so on.
However, existing web break detection systems only monitor the “normal operation” for a web break, specifically when the material web has already been threaded. Various types of web break detector are known, for example based on detecting the web speed (cf., for example, DE 101 57 914 A1), the detection of a temperature change (cf., for example, DE 101 31 281 A1), the optical detection of surface characteristics (cf., for example, DE 201 03 070 U1 and DE 42 16 653 C2) and the detection of pressures or pressure changes in connection with a vacuum web guiding device, in particular suction roll (cf., for example, EP 0 660 898 B1 and DE 100 31 163 A1). Conventionally, break monitoring is therefore not effective or is deactivated during tail widening. If a break occurs during tail widening, this must be detected by the operating personnel and it is then necessary for all the measures to be initiated manually in order to avoid damage to the machine and in order to be able to re-thread (to transfer) the material web. This applies in spite of the fact that, in modern papermaking machines, the aim is generally to increase the production efficiency. What stands in the way of automatic web break detection is the thought that the introduction of the transfer strip into the machine and tail widening are transient, not steady state, processes or states, which should be monitored better by human beings for greater reliability.